CORAL ALGAE 203 



occurrence in large quantities in various localities in the 

 Indian Ocean. 



Many other examples could be given to illustrate the 

 wide distribution of this genus of calcareous Algae and of its 

 importance in forming and protecting the bed of the sea 

 in shallow waters. It extends from the Arctic seas to the 

 coral reefs of the Tropics, and wherever the conditions of 

 the tides and sea-currents are favourable for its growth, 

 whether in the cold waters of the arctic regions or the warm 

 waters of the equatorial regions, it seems to dominate the 

 position. 



LiTHOPHYLLUM. — The genus Lithophyllum is another 

 calcareous Alga which is usually found encrusting rocks, 

 corals, and other animal and vegetable growths, following 

 the irregularities of its support and throwing up papilliform 

 or dome-shaped tubercles from its upper free surface. It 

 frequently becomes free by detachment from its original 

 support and then forms spherical or irregular lumps that 

 are rolled by the surf. Like other Rhodophyceae the living 

 coral has a pink or red colour, but specimens of Lithophyllum 

 which are dried and dead are nearly always white in contrast 

 to the specim.ens of Lithothamnion, which when dried usually 

 but not always retain a reddish colour. The specimens of 

 this genus often attain to very great dimensions, and on some 

 of the coral reefs of the Tropics form huge, massive or en- 

 crusting growths covering the greater part of the rocks 

 exposed to the breakers. There can be no doubt whatever 

 as to the very important part that is played by Algae of this 

 genus in the building up of the coral reefs, and in protecting 

 them from v.^ave action and other destructive agencies. 



The genus Lithophyllum is more prevalent in the warmer 

 than in the colder seas, but specimens are found in all the 

 great sea areas, e.g. Lithophyllum (G) hrassica florida'^ in the 

 Mediterranean and Lithophyllum lichenoides of the British 

 seas. 



It has already been mentioned that there is no character 

 which can be readily determined by the field naturalist or 



^ I have included in this account of Lithophyllum the species attri- 

 buted to the genus Goniolithon by Foslie. Vide infra, p. 205. 



